Carb Question for 360

[Root2812]

Hi guys... First I want to admit that I know nothing about 4 barrel carbs. I have rebuilt the 1 barrel on my 1950 Chevy and the one on my lawn mower but that's it. I hope you guys can give me some advice.

My car is a 1974 roadrunner with the HP 360 4 barrel. I believe the engine to be original but I am not sure. The carb appears to be from a late 70's truck I think. The numbers I found on this Holley carb say its a 650 cfm and the internet says it was a quadrajet replacement on late 70's trucks.

I dug up this schematic (page 5) online so please reference it since I don't know what anything does I'll just list the number on the picture.
http://documents.holley.com/199r8340-1rev.pdf

My car runs ok now but its symptoms always change. I know it sat for the better part of 5 years before I got it. First it started and idled great but was kinda a dog. Then after my dad screwed with some stuff on the carb ( think it may only have been the fuel level check plug) it didn't idle as well but it hauled ***. Coul it have been trash in the carb? My choke has been sticking too so I am sure that's a problem. I was looking it over and found a piece of linkage was missing (part 22) that pushed a thing down on the carb. I am not sure what this is and have no idea where to find one.

Also if you look infront of that part on the carb there is a small tower like thing that is one both the front and rear bowl. The carb is leaking out of the top of both of those. Someone at some point put jbweld or something over them to stop the leak but I stopped the leak with a duel resistant silicone.

Please help me figure out what to do.

Also If I bite the bullet and but a new carb I was thinking of getting Edlebrock. I want good power but also good drivability with my 3.55 gears. What cfm would you all recommend? 600? Also is this a spread bore carb? Then there are a bunch of option that I don't understand like mechanical or vacuum secondary's, choke type, ect. I think my choke is controlled by a spring or something in the manifold so is that manual choke or no? I know its not electric.

Thanks Guys. Sorry to be the guy who knows nothing.

 

[WileERobby]

Put what originally came on your car... a Thermoquad.

 

[62 Dart Convertible]

No need to apologise for not knowing much - everybody starts off knowing nothing.

As WileERobby states, he still knows nothing.

He is a little harsh on himself though as he also correctly states your car originally came with a Carter Thermoquad, which is a spreadbore carb, as is your Holley. Thermoquads are a great carb, but rather complicated to set up well by the uninitiated, thus the reason so many go the easier option of using a Holley when trouble first strikes. I would get to the bottom of what is wrong with your carb before giving up and sourcing a good Thermoquad.

From your description, sounds like your choke is automatic type. The spring on your manifold is a bi-metal spring that twists according to temperature, so opens the choke plate (120) as engine warms up. They need to be adjusted correctly to work well and are notorious for sticking/binding as such small forces are involved. It works in conjuction with choke vacuum diaghram (75) that opens the choke a minimum amount when cranking/idling and prevents flooding/over enrichment when cold.

Your carb is a vacuum secondary model, and that is best for a stock/mild street car. Holleys are divided into vacuum secondaries or mechanical secondaries types. Vac sec is where when you floor it, the secondaries opening is acuated by a vacuum diaphragm (112, 115, 117 etc) which eliminates bogging/flat spots by not opening them more than they need to be - best for the street. Holley mech sec carbs will open the secondaries (irrespective of engine speed) given a heavy enough right foot which is not ideal for your car. As a side note, all Carter/Edelbrock carbs have mechanical secondaries too, but contain another valve to eliminate bogging/flat spots so are suited to a street car, unlike Holley mech sec carbs that are meant for performance/racing.

What is the Holley List number stamped on the drivers side of the choke horn?

The instruction sheet you posted is for a large cross section of carb models so many parts pictured may or may not be same as yours.

Part 22 is the rod that opens/closes the primary fuel bowl vent valve according to throttle position - a feature on emissions carbs that limit the gas fumes escaping to atmosphere. If it's missing, it should not be hard to find one... (carb repairers, eBay etc) It's a Holley - common as muck.

The page 5 exploded view shows 3 different types of primary fuel bowls (4). The one on the right is the centre hung float style, and allows bowl fuel level adjustment without removing bowl via the nut (14) and lock screw (12). The other 2 bowl types on the left are side hung float style and fuel level is not externally adjustable. Bowl fuel level is set by correctly bending a tab on the float whilst dismantled. When you say there is a tower on the bowl that leaks fuel, it sounds like it's from a level adjustment nut/lock screw, but the side hung float bowl is the only one pictured with a bowl vent valve, so I'm confused as to which style you have. JB weld or silicon sealant on a carb is dodgy - leaks are either from gasket/seal failure or cracked/bent/broken parts.

Post a pic of your carb.

Holleys are inexpensive, simple, robust, common, and they're easily rebuilt. If you chose to have a go at rebuilding this one, you could not start with a simpler 4 barrel. If you don't feel up to it, get some quotes on it rebuilt by a good carb shop. If it is uneconomical, look at changeover or even new Holley spreadbores. Or find a correct model rebuilt Thermoquad. Spread bores are great for a street car as the small primaries give good economy at light throttle, and big secondaries for making power when you're on it. 650 CFM is a great size Holley for your engine, and vac sec carbs are quite forgiving if you did over size your carb for your engine (i.e. if you went larger).

 

[rumblefish360]

IF! You purchase an Edelbrock carb, get the AVS style they call the "Thunder Series" carb. It has the tuneable secondary air door. The weighted door of the AFB tends to give a problem when the throttle is floor quickly. The weighted door opens up to fast for the engines needs. You big down. (Go real lean for a second)

I use the 650 AVS Thunder on my '79 Magnum w/a 360/727/3.55.

 

[Root2812]

Thanks for all that info. It sounds like I should try a rebuild. My carb is list number 7855.



The spot that was leaking is that raised area next to that vent. You can see the job weld over the top of it.

 

[318willrun]

As mentioned, your car came with a TQ. Your current carb would replace a Q-jet/TQ (both carbs are very similar when looking at the bottoms). You could rebuild your current carb, and I bet it wouldn't be as bad as your thinking. Kit's are pretty cheap on ebay. It would be worth a try, in my opinion. If ya did one on your '50 chevy, I bet you get this done with no issues. You tube can offer a few "visuals" as well..... Good luck!